The effect of halothane, enflurane, and isoflurane on the dynamic stiffness of rabbit papillary muscle

The authors examined the effect of halothane, enflurane, and isoflurane on the dynamic stiffness of rabbit papillary muscles in Ba²⁺ contracture. Ca²⁺ was replaced by Ba²⁺ in order to constantly activate myofibrils. The dynamic stiffness of the contractured muscle was examined by exposing the muscle to sinusoidal length perturbations at frequencies of 0.05-30 Hz under two concentrations of anesthetic, approximately 0.5, and 1.5-2 mM, and at two Ba²⁺ concentrations, 0.5 and 1.5-2 mM. The anesthetics had no effect on the frequency (f(min)) at which minimum stiffness occurred, but markedly decreased the stiffness modulus at high frequencies (K(hi)). The decrease in K(hi) was significant for all anesthetics at the P < 0.05 level. Increasing the Ba²⁺ concentration from 0.5 to 1.5-2 mM in the presence of 0.5 mM of anesthetic resulted in a return of K(hi) to control levels. The authors conclude that halothane, enflurane, and isoflurane did not alter actin-myosin ATPase kinetics, because f(min) was unchanged, but decreased the number of crossbridge interactions, because K(hi) was significantly decreased by all three anesthetics.